As one developing apparatus using a single-component developer is known an apparatus in which a thin layer of developer is formed on a developer support member disposed facing a support member for an electrostatic latent image, and the latent image is developed by transferring developer from the developer support member to the electrostatic image in the developing area where the developer support member faces the latent image support member.
In such a developing apparatus, the developer stored in a housing is supplied to the surface of the developer support member and then transported by the rotation of the surface. The developer support member has an opening in the housing toward the electrostatic latent image support member, and it comes into proximity with the electrostatic latent image support member at this point.
In this kind of apparatus, if developer leaks from the margins of the image area along the axis of the developer support member or through the space between the developer support member and the housing, it splashes outside the developing apparatus, causing problems such as making other portions of the image forming apparatus dirty. To prevent this, for example, Japanese unexamined utility model publication Hei 1-164456 (1989), Japanese unexamined patent publication Hei 2-43582 (1990), Japanese unexamined patent publication Hei 2-302770 (1990), Japanese unexamined patent publication Hei 3-4255 (1991) and Japanese unexamined patent publication Hei 3-61971 describe developing apparatuses having side seal members at both ends along the axis of the developer support member to prevent the leakage. All these developing apparatuses use a porous elastomer, a felt type material or the like as side seal members and fill the spaces between the developer support member and the housing with them to prevent leakage.
One such developing apparatus has the above described side seal members and a blade contacting the developer support member under pressure and used as a developer controlling means for controlling the quantity of developer on the developer support member and forming a thin layer of developer.
FIG. 6 illustrates an example of such a developing apparatus. In it, (a) is a cross-sectional view orthogonal to the axis of the developer support member and (b) is a longitudinal-sectional view along the axis of the developer support member.
In this developing apparatus, a developer support member 101, a blade 102 which contacts it under pressure, a mixing and transporting member 105 which provides developer to the surface of the developer support member by rotating in the developer storage compartment are provided in housing 104. Developer is transferred from one end portion along the axis of the developer support member through a developer transport chamber 109.
In this developing apparatus, as shown in FIG. 7(a) and (b), side seal members 103 are provided so that they contact the round surface of the developer support member 101 under pressure and are pressed to match both ends of blade 102. By applying side seal members between inside of the housing 104 and the developer support member, leakage of developer from around both end portions of the developer support member is prevented. If the pressing force of the side seal members 103 toward the end portions of the blade 102 is small, a space may be formed between them by the distortion (contraction) of the side seal members 103 or errors in positioning, which may lead to a leakage of developer. To prevent this, side seal members 103 are brought into contact with the blade 102 under sufficient pressure to provide some distortion.
Forming side seal members 103 to match both end portions of the blade 102 makes them easy to fit and facilitates the production process.
The side seal members 103 have, in many cases, a felt material 103a made from wool, tetron or nylon, and a sliding material 103b contacting the developer support member made of a felt of fluorine-based resin. As side seal members made of wool tend to distort significantly in repeated use, causing a space between the developer support member as shown in FIG. 7(c), which may lead to leakage of developer, sometimes polyurethane foam is used instead.
A developing apparatus having side seal members pressed to match both end portions of the blade, which is a developer controlling member, however, has the following problems.
Usually, in addition to the force pressing the side seal members to the developer support member and the frictional force between the side seal members and the round surface of the developer support member, the side seal members are also subject to a pressing force toward the blade. If the pressing force of the side seal members 103 toward the end portions of the blade 102 is strong, a flat spring 102a of the blade distorts as shown in FIG. 8(a), and the contact pressure of the elastomer 102b toward the developer support member 101 is not uniform. With such non-uniformity of contact pressure, non-uniformity in the thin layer of developer formed on the developer support member 101 occurs, resulting in a striped non-uniform image density.
If over time, wear occurs in the elastomer 102b of the blade sliding on the surface of the developer support member 101, and if the contact force of the side seal members 103 to match the blade 102 is strong, displacement of the blade 102 is constrained, resulting in an inadequate and unstable contact force of the blade toward the surface of the developer support member 101 as shown in FIG. 8(b). This leads to failures in the formation of the layer of developer around the developer support member and to defects in images.
Developing apparatus having these problems must be replaced even if there are no problems in other portions and functions, which may shorten the life of the developing apparatus.